Recessing trench to target depth using feed forward data

ABSTRACT

Recessing a trench using feed forward data is disclosed. In one embodiment, a method includes providing a region on a wafer including a trench area that includes a trench and a field area that is free of any trench, and a material applied over the region so as to fill the trench in the trench area and form a step between the trench area and the field area; etching to partially etch the trench; determining a target etch duration (t D ) for etching to the target depth (D T ); and etching the trench to the target depth (D T ) for a period approximately equal to the target etch duration (t D ). The target etch duration t D  may be fed forward for recessing another trench to the target depth D T . The method does not require a send ahead wafer, is fully compatible with conventional automated processes and provides in-situ etch time correction to each wafer.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates generally to semiconductor device fabrication, andmore particularly, to recessing a material in a trench to a targetdepth.

2. Background Art

A common process in trench technology is filling a trench with a fillingmaterial and then recessing the filling material to a predetermineddepth. For example, to form a buried plate of a trench capacitor, anarsenic-doped glass (ASG) layer is deposited on a trench sidewall andthe trench is filled with resist. The resist is then recessed to apredetermined depth to expose the ASG in the upper trench. The exposedASG is then selectively removed to the resist in the lower trench. Theresist is then removed from the trench, leaving ASG only on the lowertrench sidewall. Arsenic in the ASG is then driven into the siliconsubstrate in a subsequent thermal process to form the buried plate—aheavily doped region in the substrate.

One challenge in this process is precisely controlling the depth of theresist recess, which is critical to determining device characteristicssuch as trench capacitance and parasitic leakage current. One approachto this challenge includes a ‘send ahead’ technique in which a waferfrom a lot is processed first and the recess depth is measured. Theprocess for the rest of the wafers is then adjusted based on themeasured depth from the ‘send ahead’ wafer. The ‘send ahead’ approachhas a number of disadvantages. First, it is destructive because theresist recess of the send ahead wafer is traditionally measured by ascanning electron microscope (SEM), which requires the send ahead waferto be cleaved (destroyed) for SEM analysis. This approach isprohibitively costly. Second, the ‘send ahead’ approach istime-consuming. When a lot gets to the recess process, a send aheadwafer has to be split from the lot and processed first and the processis adjusted based on the send ahead. The turn-around-time for this sendahead approach may take several hours. Third, the process delay betweenthe send ahead and the lot adds process variation since a condition ofthe recess chamber from which the send ahead wafer is pulled may changewhen the lot is processed. Fourth, the send ahead approach is notcompatible with the currently automated 300 mm process because itrequires dedicated manpower to take the send ahead wafer out of the lot,deliver it to SEM lab, and analyze the recess depth after the SEM iscompleted. Finally, the send ahead approach cannot accommodate incomingwafer-to-wafer variations such as variations of trench profile and thefilling characteristics. The possible chamber condition changeaggravates this situation. All these variations cause the recess depthvariation from wafer to wafer. With the send ahead approach, the processis adjusted only once and then all wafers are processed with the sameprocess setup. Accordingly, process adjustment to accommodate the abovevariation on each wafer is impossible using the send ahead approach.

Therefore, a simple process with precise recess control but without sendahead is desired.

SUMMERY OF THE INVENTION

Recessing a trench using feed forward data is disclosed. In oneembodiment, a method includes providing a region on a wafer including atrench area that includes a trench and a field area that is free of anytrench, and a material applied over the region so as to fill the trenchin the trench area and form a step between the trench area and the fieldarea; etching to partially etch the trench; determining a target etchduration (t_(D)) for etching to the target depth (D_(T)); and etchingthe trench to the target depth (D_(T)) for a period approximately equalto the target etch duration (t_(D)). The target etch duration t_(D) maybe fed forward for recessing another trench to the target depth D_(T).The method does not require a send ahead wafer, is fully compatible withconventional automated processes and provides in-situ etch timecorrection to each wafer.

A first aspect of the invention provides a method of recessing a trenchto a target depth (D_(T)), the method comprising the steps of: providinga region on a wafer including a trench area including a trench and afield area that is free of any trench, a material applied over theregion so as to fill the trench in the trench area and form a stepbetween the trench area and the field area; first etching the materialuntil a surface of the wafer in the trench area is exposed; secondetching the material until the surface of the wafer in the field area isexposed; determining a target etch duration (t_(D)) for a third etchingfor recessing the trench to the target depth; and third etching thetrench to the target depth (D_(T)) for a period approximately equal tothe target etch duration (t_(D)).

A second aspect of the invention provides an etching system forrecessing a trench to a target depth (D_(T)), the system comprising: anetching chamber for etching a region on a wafer including a trench areaincluding at least one trench and a field area that is free of anytrench, a material applied over the region so as to fill the at leastone trench in the trench area and form a step between the trench areaand the field area; wherein the etching includes first etching thematerial until a surface of the wafer in the trench area is exposed, andsecond etching the material until the surface of the wafer in the fieldarea is exposed; a determinator for determining a target etch duration(t_(D)) for a third etching for recessing the at least one trench to thetarget depth; and a communicator for feeding forward the target etchduration (t_(D)) for the third etching for recessing another trench tothe target depth (D_(T)).

A third aspect of the invention provides a program product stored on acomputer-readable medium, which when executed, controls recessing of atrench to a target depth (D_(T)), the program product comprising:program code for controlling etching of a region on a wafer including atrench area including at least one trench and a field area that is freeof any trench, a material applied over the region so as to fill the atleast one trench in the trench area and form a step between the trencharea and the field area; wherein the etching includes first etching thematerial until a surface of the wafer in the trench area is exposed andsecond etching the material until the surface of the wafer in the fieldarea is exposed; program code for determining a target etch duration(t_(D)) for a third etching for recessing the at least one trench to thetarget depth; and program code for feeding forward the target etchduration (t_(D)) for the third etching for recessing at least one trenchto a target etch depth (D_(T)).

The illustrative aspects of the present invention are designed to solvethe problems herein described and/or other problems not discussed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will be more readilyunderstood from the following detailed description of the variousaspects of the invention taken in conjunction with the accompanyingdrawings that depict various embodiments of the invention, in which:

FIG. 1 shows an etching system for recessing a trench to a target depth(D_(T)) using feed forward of data according to one embodiment of theinvention.

FIGS. 2-5 show stages of etching according to one embodiment of theinvention.

FIG. 6 shows an endpoint trace according to one embodiment of theinvention.

It is noted that the drawings of the invention are not to scale. Thedrawings are intended to depict only typical aspects of the invention,and therefore should not be considered as limiting the scope of theinvention. In the drawings, like numbering represents like elementsbetween the drawings.

DETAILED DESCRIPTION

Turning to the drawings, FIG. 1 shows one embodiment of an etchingsystem 10 for recessing a trench to a target depth (D_(T)) using feedforward of data according to the invention. Etching system 10 includesan etching chamber 12 for etching a region 14 on a wafer 16. Etchingchamber 12 may include any now known or later developed structures foretching material on wafer 16, e.g., wet etching structure, plasmaetching structure, chemical downstream etching structure, reaction ionetching structure, etc. As shown in FIG. 2, region 14 includes a trencharea 20 including at least one trench 22 and a field area 24 that isfree of any trench. A material 26 is applied over region 14 so as tofill at least one trench 22 in trench area 20 and form a step 28 betweentrench area 20 and field area 24. In one embodiment, material 26 mayinclude a photoresist or any other material now known or later developedfor use in filling a trench. Wafer 16 may also include a pad layer 29of, for example, silicon nitride with an underlying silicon dioxide.

As is described in greater detail herein, and as shown in FIG. 1,etching system 10 also may include an etch controller system 30 forcontrolling recessing of a trench according to the invention. Etchingsystem 10 may access a measurer 32 such as an atomic force microscope(AFM) for measuring a height H_(S) of step 28 (FIG. 2). Etch controllersystem 30 may include a computer infrastructure 102 that can perform thevarious process steps described herein, inter alia, for recessing atrench to a target depth (D_(T)). In particular, computer infrastructure102 is shown including a computing device 104 that comprises an etchcontroller 106, which enables computing device 104 to control theprocess steps of the invention.

Computing device 104 is shown including a memory 112, a processor unit(PU) 114, an input/output (I/O) interface 116, and a bus 118. Further,computing device 104 is shown in communication with an external I/Odevice/resource 120 and a storage system 122. As is known in the art, ingeneral, processor unit 114 executes computer program code, such as etchcontroller 106, which is stored in memory 112 and/or storage system 122.While executing computer program code, processor 114 can read and/orwrite data, such as etching parameter data, to/from memory 112, storagesystem 122, and/or I/O interface 116. Bus 118 provides a communicationslink between each of the components in computing device 104. I/O device120 can comprise any device that enables a user to interact withcomputing device 104 or any device that enables computing device 104 tocommunicate with one or more other computing devices.

In any event, computing device 104 can comprise any general purposecomputing article of manufacture capable of executing computer programcode installed by a user (e.g., a personal computer, server, handhelddevice, etc.). However, it is understood that computing device 104 andetch controller 106 are only representative of various possibleequivalent computing devices that may perform the various process stepsof the invention. To this extent, in other embodiments, computing device104 and etch controller 106 can comprise any specific purpose computingarticle of manufacture comprising hardware and/or computer program codefor performing specific functions, any computing article of manufacturethat comprises a combination of specific purpose and general purposehardware/software, or the like. In each case, the program code andhardware can be created using standard programming and engineeringtechniques, respectively.

Similarly, computer infrastructure 102 is only illustrative of varioustypes of computer infrastructures for implementing the invention. Forexample, in one embodiment, computer infrastructure 102 comprises two ormore computing devices (e.g., a server cluster) that communicate overany type of wired and/or wireless communications link, such as anetwork, a shared memory, or the like, to perform the various processsteps of the invention. When the communications link comprises anetwork, the network can comprise any combination of one or more typesof networks (e.g., the Internet, a wide area network, a local areanetwork, a virtual private network, etc.). Regardless, communicationsbetween the computing devices may utilize any combination of varioustypes of transmission techniques.

As previously mentioned and discussed further below, etch controller 106enables computing infrastructure 102 to control recessing of a trench toa target depth D_(T). To this extent, etch controller 106 is shownincluding: conventional etch parameter controller 130, a determinator132 for determining a target etch duration t_(D) for recessing thetrench to target depth D_(T), a communicator 134 for feeding forwardtarget etch duration t_(D) for recessing another trench to target depthD_(T), and a recorder 136 for recording an etch duration t of apredetermined part of an etching process. Operation of each of theabove-described systems is discussed further below. However, it isunderstood that some of the various systems shown in FIG. 1 can beimplemented independently, combined, and/or stored in memory for one ormore separate computing devices that are included in computerinfrastructure 102. Further, it is understood that some of the systemsand/or functionality may not be implemented, or additional systemsand/or functionality may be included as part of the environment ofetching system 10. Conventional etch parameter controller 130 mayinclude any functionality known to those skilled in the art as beingprovided with a conventional etch system for controlling etching ofregion 14. Operational structure of etch chamber 12 has not beenillustrated for clarity.

Turning to FIGS. 2-6, various embodiments of a method of recessing atrench to target depth D_(T) using feed forward of data and etchcontroller system 30 will now be described. In a first step, as shown inFIG. 2, region 14 on wafer 16 including trench area 20 having at leastone trench 22, and field area 24 that is free of any trench 22, isprovided. In one embodiment, trench area 20 includes an array oftrenches, but this is not necessary. In addition, material 26, e.g., aphotoresist or other fill material, is applied over region 14 so as tofill at least one trench 22 in trench area 20 and form step 28 betweentrench area 20 and field area 24. Step 28 has a height H_(S) that can bemeasured by a profilometer such as an atomic force microscope (AFM). Inone embodiment, wafer 16 may include a pad layer 29 which may include asilicon nitride and an underlying silicon dioxide.

FIGS. 2-5 show various stages of etching at least one trench 22. Thetype of etching conducted, e.g., reactive ion etching, wet etching,plasma etching, downstream etching, etc., is not described in detailherein because it varies depending on the material being etched and iswithin the purview of one with skill in the art. As shown in FIG. 6, asthe etching stages proceed, recorder 136 (FIG. 1) may record durationsof the different stages and/or generate an endpoint trace 150 of theetching. That is, recorder 136 may perform endpoint tracing and monitorthe trace of the etching stages to determine an endpoint of each etchingstage. As known in the art, an “endpoint trace” can be generated bymonitoring the trace of emissions from a reactive species or volatileproduct using optical emission during etching, which changes asdifferent materials are etched. A change in endpoint trace 150 indicatesa change in materials that are being etched, and hence different stagesof the etching, the durations of which can be determined readily fromendpoint trace 150. For example, in FIG. 6, a first dip 152 indicatesthat the etching has reached pad layer 29 in trench area 20, as shown inFIG. 3. First dip 152 may be caused by all resist material 26 in trencharea 20 above pad layer 29 being removed and pad layer 29 being exposed.

In a first etching 160, shown in FIG. 3, material 26 is etched until asurface 162 of wafer 16 in trench area 20, e.g., pad layer 29, isexposed. Recorder 136 (FIG. 1) may record that etching 160 has an etchrate R₀ and a duration t₀, as indicated in FIG. 6. That is, recorder 136may monitor endpoint trace 150 of first etching 160 to determine anendpoint of the etching step. As shown in FIG. 4, a next stage ofetching 164 includes etching material 26 until a surface 166 of wafer 16in field area 24 is exposed. Simultaneously, trench(es) 22 are etched toa first depth D₁, which is less than target depth D_(T). As indicated inFIG. 6, recorder 136 (FIG. 1) may record that etching 164 has an etchrate R₁ in trench area 20 and an etch rate R_(F) in field area 24 and aduration t₁, i.e., recorder 136 may monitor endpoint trace 150 of secondetching 164 to determine an endpoint of the etching step.

A next step of the method includes determinator 132 (FIG. 1) determininga target etch duration t_(D) for etching 168 (FIG. 5) for recessingtrench(es) 22 to target depth D_(T). As shown in FIG. 5, etching 168recesses material 26 (now only in trench(es) 22) until target depthD_(T) is achieved in trench(es) 22. Target depth D_(T) is the sum offirst depth D₁ and a second depth D₂, the latter achieved by etching168, i.e., D_(T)=D₁+D₂. As indicated in FIG. 6, recorder 136 (FIG. 1)may record that etching 168 has an etch rate R₂ in trench area 20 and aduration t₂. Note that etch rate R₂ may be greater than etch rate R₁ intrench area 20 at the same etching conditions because of the absence ofmaterial 26 in field area 24. All etch rates can be predetermined basedon conventional techniques, e.g., based on known etch rates of knownetch chemistries. Note that target etch duration t_(D) corresponds toetch duration t₂ in FIG. 6. In a first embodiment, determinator 132 maydetermine target etch duration t_(D) according to the followingequation:t _(D)=(D _(T) −R ₁ t ₁)/R ₂  (1)

As noted above, t₁ is the duration of etching 160 (FIG. 3), R₁ is theetch rate of trench area 20 during etching 164 (FIG. 4) and R₂ is theetch rate of trench area 24 during etching 168 (FIG. 5). The aboveequation is derived from the knowledge that first depth D₁=R₁t₁, seconddepth D₂=R₂t₂, where t_(D) and t₂ are equivalent, and D_(T)=D₁+D₂.

In another embodiment, determinator 132 (FIG. 1) determines target etchduration t_(D) according to the following equation:t _(D)=(D _(T) −H _(s) R ₁ /R _(F))/R ₂  (2)

As noted above, H_(S) is the height of step 28 (FIG. 2), R₁ is the etchrate of trench area 20 during etching 164 (FIG. 4), R₂ is the etch rateof trench area 20 during etching 168 (FIG. 5) and R_(F) is the etch rateof field area 24 during etching 168 (FIG. 5). The above equation isderived from the knowledge that first depth D₁=R₁t₁, second depthD₂=R₂t₂, step height H_(s)=R_(F)t₁ where t_(D) and t₂ are equivalent,and D_(T)=D₁+D₂. This embodiment requires measurer 32 (FIG. 1) tomeasure height H_(S) of step 28 (FIG. 2), but it does not requireinformation from the endpoint trace as all variables for calculatingt_(D) based on equation (2) are known.

A final step includes etching 168 (FIG. 5) in trench(es) 22 to targetdepth (D_(T)) for a period approximately equal to target etch duration(t_(D)). This step may also include communicator 134 feeding forwardtarget etch duration t_(D) for etching 168 (FIG. 5) for recessing thesame trench or another trench in wafer 16 or another wafer 170 (FIG. 1)to target depth D_(T). The implementation of communicator 134 may varydepending on the environment. For example, communicator 134 may simplybe an internal recordation for use in etching other regions of wafer 16in etch chamber 12, or it may include some form of communicationmechanism, e.g., a network, for feed forwarding data to other etchchambers (not shown).

It is understood that the order of the above-described steps is onlyillustrative. To this extent, one or more steps can be performed inparallel, in a different order, at a remote time, etc. Further, one ormore of the steps may not be performed in various embodiments of theinvention.

While shown and described herein as a method and system for recessing atrench to a target depth D_(T) using feed forward of data, it isunderstood that the invention further provides various alternativeembodiments. For example, in one embodiment, the invention provides acomputer-readable medium that includes computer program code to enable acomputer infrastructure to control recessing of a trench to target depthD_(T) using feed forward of data. To this extent, the computer-readablemedium includes program code, such as etch controller 106 (FIG. 2),which implements each of the various process steps of the invention. Itis understood that the term “computer-readable medium” comprises one ormore of any type of physical embodiment of the program code. Inparticular, the computer-readable medium can comprise program codeembodied on one or more portable storage articles of manufacture (e.g.,a compact disc, a magnetic disk, a tape, etc.), on one or more datastorage portions of a computing device, such as memory 112 (FIG. 2)and/or storage system 122 (FIG. 2) (e.g., a fixed disk, a read-onlymemory, a random access memory, a cache memory, etc.), and/or as a datasignal traveling over a network (e.g., during a wired/wirelesselectronic distribution of the program code).

In another embodiment, the invention provides a business method thatperforms the process steps of the invention on a subscription,advertising, and/or fee basis. That is, a service provider, such as anApplication Service Provider, could offer to control recessing a trenchto a target depth (D_(T)) using feed forward of data on a remote etchchamber 12 (FIG. 1), as described above. In this case, the serviceprovider can manage (e.g., create, maintain, support, etc.) a computerinfrastructure, such as computer infrastructure 102 (FIG. 1), thatperforms the process steps of the invention for one or more customers.In return, the service provider can receive payment from the customer(s)under a subscription and/or fee agreement and/or the service providercan receive payment from the sale of advertising space to one or morethird parties.

In still another embodiment, the invention provides a method ofgenerating a system for controlling recessing a trench to a target depth(D_(T)) using feed forward of data. In this case, a computerinfrastructure, such as computer infrastructure 102 (FIG. 1), can beobtained (e.g., created, maintained, having made available to, etc.) andone or more systems for performing the process steps of the inventioncan be obtained (e.g., created, purchased, used, modified, etc.) anddeployed to the computer infrastructure. To this extent, the deploymentof each system can comprise one or more of (1) installing program codeon a computing device, such as computing device 104 (FIG. 1), from acomputer-readable medium; (2) adding one or more computing devices tothe computer infrastructure; and (3) incorporating and/or modifying oneor more existing systems of the computer infrastructure, to enable thecomputer infrastructure to perform the process steps of the invention.

As used herein, it is understood that the terms “program code” and“computer program code” are synonymous and mean any expression, in anylanguage, code or notation, of a set of instructions intended to cause acomputing device having an information processing capability to performa particular function either directly or after any combination of thefollowing: (a) conversion to another language, code or notation; (b)reproduction in a different material form; and/or (c) decompression. Tothis extent, program code can be embodied as one or more types ofprogram products, such as an application/software program, componentsoftware/a library of functions, an operating system, a basic I/Osystem/driver for a particular computing and/or I/O device, and the like

The foregoing description of various aspects of the invention has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and obviously, many modifications and variations arepossible. Such modifications and variations that may be apparent to aperson skilled in the art are intended to be included within the scopeof the invention as defined by the accompanying claims.

1. A method of recessing a trench to a target depth (D_(T)), the methodcomprising the steps of: providing a region on a wafer including atrench area including a trench and a field area tat is free of anytrench, a material applied over the region so as to fill the trench inthe trench area and form a step between the trench area and the fieldarea; first etching the material until a surface of the wafer in thetrench area is exposed; second etching the material until the surface ofthe wafer in the field area is exposed; measuring a height of the step(H_(S)); determining a target etch duration (t_(D)) for a third etchingfar recessing the trench to the target depth; and third etching thetrench to the target depth (D_(T)) for a period approximately equal tothe target etch duration (t_(D)).
 2. The method of claim 1, wherein thematerial includes a photoresist.
 3. The method of claim 1, furthercomprising the step of recording a first etch duration (t₁) of thesecond etching.
 4. The method of claim 3, wherein the target etchduration (t_(D)) determining step includes determining the target etchduration (t_(D)) according to the following equation:t _(D)=(D _(T) −R ₁ t ₁)/R ₂, wherein R₁ is a first etch rate of thetrench area during the second etching and R₂ is a second etch rate ofthe trench area during the third etching.
 5. The method of claim 1,wherein the target etch duration (t_(D)) determining step includesdetermining the target etch duration (t_(D)) according to the followingequation:t _(D)=(D _(T) −H _(S) R ₁ /R _(F))R ₂, wherein H_(S) is a height of thestep, R₁ is a first etch rate of the trench area during the secondetching, R₂ is a second etch rate of the trench area during the thirdetching and R_(F) is a third etch rate of the field area during thesecond etching.
 6. The method of claim 1, further comprising feedingforward the target etch duration (t_(D)) for the third etching forrecessing another trench to the target depth (D_(T)).
 7. The method ofclaim 1, wherein the trench area includes an array of trenches.
 8. Themethod of claim 1, further comprising monitoring an endpoint trace ofeach the first and second etching steps to determine an endpoint of eachetching step.